[MLModel]

It's still a bug in 5.9 on 10.5.6. The following gives an AppleEvent failure:

set the active tab of the front browser to the last tab of the front browser

and many permutations on the relevant vocabulary do the same. What's particularly irksome is that it leaves no way in applescript to create a new tab at the end of the a browser's current ones then make that one the active one for that browser. It worked in OW 5.0, April 2005 and possibly later than that.